This invention relates to an electrode for projection welding, utilized in a field where a shaft-like part such as a bolt is inserted in an electrode receiving hole and welded.
FIG. 1 is a view showing an embodiment of the invention, but the prior art will be described using this figure. The attaching portion of an electrode collectively indicated by the reference numeral 1 is formed with a cooling hole 13 into which cooling water is introduced; the cooling water which has flowed thereinto flows back as shown by an arrow. An end cover 10 to which heat is directly transmitted during welding is positioned at a place remotest from the cooling hole 13. Further, inserted in the main body 6 is a guide sleeve 12 made of non-metallic material made of synthetic resin.
When the end cover 10 which becomes hottest in the entire electrode is isolated greatly from the cooling hole 13, as described above, the cooling action is not very effective for the end cover 10. If the end cover 10 is placed under high temperature, a phenomenon develops in which the pressing during welding will cause the flange 4 of a part to cut into the surface of the end cover 10, forming a dent in the shape of the flange 4 in the end cover 10. Therefore, the durability of the end cover 10 decreases, resulting in a short cycle of replacement of the end cover 10, greatly increasing the frequency of stoppage of the production line for replacement purposes, leading to a decrease in productivity, and to uneconomicality in the cost of replacement parts.
Further, the guide sleeve 12, which is made of non-metallic material such as synthetic resin, requires sufficient cooling in terms of heat.
Further, although various methods are known in which a shaft-like part such as a projection bolt advanced into a receiving hole in an electrode is electrically detected to ascertain the presence of a part in a normal manner, it is necessary to realize such detection by a more reliable technique.